priority_queue<int,vector<int>,greater<int>>优先队列,按照从小到大
2016-08-20 20:31
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原网址: 优先队列
在优先队列中,优先级高的元素先出队列。
标准库默认使用元素类型的<操作符来确定它们之间的优先级关系。
优先队列的第一种用法,也是最常用的用法:
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
priority_queue<int> qi;
通过<操作符可知在整数中元素大的优先级高。
故示例1中输出结果为:9 6 5 3 2
第二种方法:
在示例1中,如果我们要把元素从小到大输出怎么办呢?
这时我们可以传入一个比较函数,使用functional.h函数对象作为比较函数。
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
priority_queue<int, vector<int>,
greater<int> >qi2;
其中
第二个参数为容器类型。
第二个参数为比较函数。
故示例2中输出结果为:2 3 5 6 9
第三种方法:
自定义优先级。
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
friend bool operator< (node n1,
node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
return n1.priority < n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
};
在该结构中,value为值,priority为优先级。
通过自定义operator<操作符来比较元素中的优先级。
在示例3中输出结果为:
优先级 值
9 5
8 2
6 1
2 3
1 4
但如果结构定义如下:
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
friend bool operator> (node n1,
node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
return n1.priority > n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
};
则会编译不过(G++编译器)
因为标准库默认使用元素类型的<操作符来确定它们之间的优先级关系。
而且自定义类型的<操作符与>操作符并无直接联系,故会编译不过。
//代码清单
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<iostream>
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<functional>
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<queue>
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
using Namespace
stdnamespace std;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
friend bool operator< (node
n1, node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
return n1.priority < n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
};
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int main()
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
const int len = 5;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int i;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int a[len] = {3,5,9,6,2};
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例1
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<int> qi;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi.push(a[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qi.top()<<" ";
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例2
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<int, vector<int>,
greater<int> >qi2;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi2.push(a[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qi2.top()<<" ";
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
q
d5d6
i2.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<node> qn;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
node b[len];
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[0].priority = 6;
b[0].value = 1;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[1].priority = 9;
b[1].value = 5;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[2].priority = 2;
b[2].value = 3;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[3].priority = 8;
b[3].value = 2;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[4].priority = 1;
b[4].value = 4;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qn.push(b[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<"优先级"<<'\t'<<"值"<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qn.top().priority<<'\t'<<qn.top().value<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qn.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
return 0;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
C++优先队列的基本使用方法
在优先队列中,优先级高的元素先出队列。标准库默认使用元素类型的<操作符来确定它们之间的优先级关系。
优先队列的第一种用法,也是最常用的用法:
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
priority_queue<int> qi;
通过<操作符可知在整数中元素大的优先级高。
故示例1中输出结果为:9 6 5 3 2
第二种方法:
在示例1中,如果我们要把元素从小到大输出怎么办呢?
这时我们可以传入一个比较函数,使用functional.h函数对象作为比较函数。
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
priority_queue<int, vector<int>,
greater<int> >qi2;
其中
第二个参数为容器类型。
第二个参数为比较函数。
故示例2中输出结果为:2 3 5 6 9
第三种方法:
自定义优先级。
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
friend bool operator< (node n1,
node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
return n1.priority < n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
};
在该结构中,value为值,priority为优先级。
通过自定义operator<操作符来比较元素中的优先级。
在示例3中输出结果为:
优先级 值
9 5
8 2
6 1
2 3
1 4
但如果结构定义如下:
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
friend bool operator> (node n1,
node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
return n1.priority > n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
};
则会编译不过(G++编译器)
因为标准库默认使用元素类型的<操作符来确定它们之间的优先级关系。
而且自定义类型的<操作符与>操作符并无直接联系,故会编译不过。
//代码清单
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<iostream>
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<functional>
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
#include<queue>
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
using Namespace
stdnamespace std;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
struct node
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
friend bool operator< (node
n1, node n2)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
return n1.priority < n2.priority;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int priority;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int value;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
};
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int main()
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
const int len = 5;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int i;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int a[len] = {3,5,9,6,2};
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例1
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<int> qi;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi.push(a[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qi.top()<<" ";
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例2
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<int, vector<int>,
greater<int> >qi2;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qi2.push(a[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qi2.top()<<" ";
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
q
d5d6
i2.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
//示例3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
priority_queue<node> qn;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
node b[len];
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[0].priority = 6;
b[0].value = 1;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[1].priority = 9;
b[1].value = 5;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[2].priority = 2;
b[2].value = 3;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[3].priority = 8;
b[3].value = 2;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
b[4].priority = 1;
b[4].value = 4;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qn.push(b[i]);
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<"优先级"<<'\t'<<"值"<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(i = 0;
i < len; i++)
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
{
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
cout<<qn.top().priority<<'\t'<<qn.top().value<<endl;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
qn.pop();
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
return 0;
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
}
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
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